Because of excellent weatherability, ozone resistance and heat resistance, ethylene/.alpha.-olefin rubber is utilized in manufacturing automotive parts, construction materials, electric wires and industrial parts. When ethylene/.alpha.-olefin rubber is used for such purposes as mentioned above, the rubber is mixed with reinforcing materials such as carbon black, fillers such as talc and clay, and compounding additives such as various softeners, vulcanizing accelerators, and vulcanizers, and the resulting mixture is kneaded in the same manner as in common rubber using a batch-wise kneading machine such as Banbury mixer or various extruders.
Since the kneading operation as mentioned above requires large energy and much time, it follows that the kneading cost necessary therefor occupies a very large proportion in the overall processing costs. Recently, in the light of the foregoing, ethylene/.alpha.-olefin rubber has come to be used widely, said rubber having a high ethylene content and a high Mooney viscosity and being difficult to knead. With the view of improving this ethylene/.alpha.-olefin rubber in kneadability, a so-called friable bale developed by inclusion in said rubber of gas has been put on the market.
In the conventional friable bale, however, there was such a drawback that because the bubbles are formed normally in a continuous state, the gas retained in said bubbles is deflated under continuous load by said bale itself and consequently the bale deteriorates in kneadability.